Thrombin is known to have a variety of activities in different cell types and thrombin receptors are known to be present in such cell types as human platelets, vascular smooth muscle cells, endothelial cells, and fibroblasts. Thrombin receptor antagonists may be useful in the treatment of thrombotic, inflammatory, atherosclerotic and fibroproliferative disorders, as well as other disorders in which thrombin and its receptor play a pathological role. See, for example, U.S. Pat. No. 6,063,847, the disclosure of which is incorporated by reference.
One thrombin receptor antagonist is a compound of the formula:

This compound is an orally bioavailable thrombin receptor antagonist derived from himbacine. Compound 11 may be synthesized from Compound 1:
wherein R5 and R6 are each independently selected from the group consisting of H, alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, aryl, alkylaryl, arylalkyl, and heteroaryl groups.
Processes for the synthesis of similar himbacine analog thrombin receptor antagonists are disclosed in U.S. Pat. No. 6,063,847, and U.S. publication no. 2003/0216437, methods of using thrombin receptor antagonists are disclosed in U.S. publication no. 2004/0192753, and the synthesis of the bisulfate salt of a particular himbacine analog is disclosed in U.S. publication no. 2004/0176418, now U.S. Pat. No. 7,235,567 the disclosures of which are incorporated by reference herein. The present application provides a novel process for preparing Compound 11 from Compound 1, which process provides an improved yield and the elimination of the need for a chiral intermediate.